Aluminum alloy for heat exchangers

ABSTRACT

An aluminum alloy for heat exchangers, the alloy, comprising a base compostion selected from a group consisting of Al-Mg-Si composition containing 0.1 to 0.8 wt % of Mg, 0.2 to 1.0 wt % of Si and 0.3 to 1.5 wt % of Mn; pure-Al composition; Al-Mg composition containing 0.05 to 1.0 wt % of Mg; and a Al-Zn composition containing 0.05 to 2.0 wt % of Zn. The alloy further comprises 0.01 to 0.3 wt % of Fe and/or 0.01 to 0.3 wt % of Ni, wherein the balance are aluminum of purity of 99.9% or higher and unavoidable impurities contained therein, and content of Cu as one of the impurities is controlled to be 0.05 wt % or less.

This application is a continuation of application Ser. No. 785,863,filed Oct. 28, 1991, which is a continuation of application Ser. No.606,712, filed Oct. 31, 1990, both abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aluminum alloy used to manufacturetubular elements or other members of heat exchangers such as thoseincorporated in radiators, car heaters, intercoolers or the likes.

2. Description of the Prior Art

The aluminum alloy "A3003" has been used in general to manufacturestructural elements such as the tubular elements which allow a heatexchanging medium to flow therethrough, because the alloy "A3003" iseasy to treat in the manufacturing processes.

Higher contents of impurities such as iron (Fe) in the aluminum alloyA3003 cause inferior corrosion resistance thereof at room temperature ornear temperatures close thereto. Efforts have been made to improve thecorrosion resistance at such lower temperatures, by making the impuritycontents as low as possible. However in this case, there arises a newproblem that intercrystalline corrosion takes place at highertemperatures including 100° C., i.e., the boiling temperature of waterand near temperatures close thereto. Corrosion of such a type causescracks in the tubular elements.

In view of those problems and particularly in a case in which water orother corrosive heat-exchanging medium is likely to be employed for theheat exchangers in radiators or the likes, tubes of aluminum alloy A3003are used as "cores" of tubular elements and their inner surfaces arecovered with a lining layer of another aluminum alloy such as "A7072" or"A5005". The alloy A7072 functions as a sacrificial anodic layer, andthe other alloy A5005 is comparatively highly corrosion-resistant.

These aluminum alloys A7075 and A5005 used as the lining layer are alsonot satisfactory because their corrosion resistance becomes worse at ornear room temperature with a rich content of Fe, and because a lower Fecontent reduced to improve the corrosion resistance at lowertemperatures will give rise to the problem of intercrystalline corrosionat higher temperature of or near 100° C.

There has been still another problem that the mechanical strength isoften lowered for instance to about 4 Kgf/mm² as a value of σ0.2 (tolerable load ) after the structural members of heat exchangers made ofthe alloy "A3003" are soldered to each other. Thus, walls constitutingthe tubular elements or other members are to be inevitably made thickerto assure sufficient strength thereof. Therefore, manufacturers haveinevitably had to accept a larger size, an excessive weight and a highermanufacture cost of the known heat exchangers. The abovementionedproblems have occurred not only in the tubular elements but also in theother structural members of heat exchangers made of such aluminumalloys.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide an aluminum alloywhich is of an improved corrosion resistance at lower temperatures in arange from about 20° C. to 50° C. ( hereinafter referred to as"low-temperature corrosion resistance") and is thus a material suited tomanufacture structural members such as tubular elements or inner lininglayers thereof in the heat exchangers.

Another object of the invention is to provide an aluminum alloy for heatexchangers which alloy is not only excellent in its low-temperaturecorrosion resistance but also is of an improved resistance tointercrystalline corrosion at higher temperatures of or near 100° C. (hereinafter referred to as "high-temperature intercrystalline corrosionresistance").

The objects are accomplished herein by providing an aluminum alloy whichcomprises: a base alloy composition selected from a first groupconsisting of a first composition containing aluminum (Al), magnesium(Mg) and silicon (Si), a second composition containing pure aluminum(Al), a third composition containing aluminum (Al) and magnesium (Mg),and a fourth composition containing aluminum (Al) and zinc (Zn);controlled amounts of one or more additional ingredients selected from asecond group consisting of iron (Fe) and nickel (Ni); and a controlledamount of copper (Cu) as an unavoidable impurity, wherein metal purityof aluminum as a major ingredient is also controlled.

In detail, the invention provides the aluminum alloy called "Al-Mg-Sialloy", "pure-Al alloy", "Al-Mg alloy" or "Al-Zn alloy" which are basedon the abovementioned first, second, third or fourth compositionrespectively.

The Al-Mg-Si alloy for heat exchangers comprises 0.1 to 0.8 wt % of Mg,0.2 to 1.0 wt % of Si, and 0.3 to 1.5 wt % of manganese (Mn), furthercomprising 0.01 to 0.3 wt % of Fe and/or 0.01 to 0.3 wt % of Ni, whereinthe balance are aluminum of purity of 99.9% or higher and unavoidableimpurities contained therein, and Cu content is controlled to be 0.05 wt% or less.

The pure-Al alloy for heat exchangers comprises 0.01 to 0.3 wt % of Feand/or 0.01 to 0.3 wt % of Ni, wherein the balance are aluminum ofpurity of 99.9% or higher and unavoidable impurities contained therein,and Cu content is controlled to be 0.05 wt % or less.

The Al-Mg alloy for heat exchangers comprises 0.05 to 1.0 wt % of Mg,further comprising 0.01 to 0.3 wt % of Fe and/or 0.01 to 0.3 wt % of Ni,wherein the balance are aluminum of purity of 99.9% or higher andunavoidable impurities contained therein, and Cu content is controlledto be 0.05 wt % or less.

The Al-Zn alloy for heat exchangers comprises 0.05 to 2.0 wt % of Zn,further comprising 0.01 to 0.3 wt % of Fe and/or 0.01 to 0.3 wt % of Ni,wherein the balance are aluminum of purity of 99.9% or higher andunavoidable impurities contained therein, and Cu content is controlledto be 0.05 wt % or less.

Other objects, features and advantages of the invention will becomeapparent from the description given hereinafter referring to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross section of a tubular element for a heat exchanger, thetubular element made of an aluminum alloy provided in the invention;

FIG. 2 is a cross section showing a modification of the tubular element;and

FIG. 3 is a perspective view showing a combined state of test piecesused in a soldering test carried out in embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Metallic or other elements contained in aluminum alloys are explained atfirst as to their functions, limited contents and the reasons why thecontents are so limited.

Al-Mg-Si alloy is suited particularly to manufacture `bare` member orcore member for tubular elements. Mg in this alloy is effective toimprove mechanical strength of soldered structural members of heatexchangers. A lower content of Mg below 0.1 wt % renders poor such aneffect whereas a higher content above 0.8 wt % causes the soldering tobecome imperfect. Thus, the most preferable range of Mg content is fromabout 0.2 to about 0.5 wt %.

Si is useful also to improve the mechanical strength of the solderedmembers. A lower content of Si below 0.2 wt % renders poor such aneffect whereas a higher content above 1.0 wt % causes the soldering tobecome imperfect. Thus, the most preferable range of Si content is above0.4 wt % but up to 0.7 wt %.

Mn improves corrosion resistance and mechanical strength of the members.A lower content of Mn below 0.3 wt % renders poor such an effect whereasthis effect is saturated with a content of or more than 1.5 wt % so thata higher content above 1.5 wt % gives no merit which can compensate anexcessively raised cost. Further, such a high content gives rise to suchcoarse crystals that will make poor the workability of the material.Therefore, Mn content must fall most preferably within a range from 0.5to 1.2 wt %.

Pure-Al alloy, Al-Mg alloy and Al-Zn alloy are particularly suited foruse as a lining material for the tubular elements.

Mg contained in Al-Mg alloy improves corrosion resistance and`sacrificial corrosion property` thereof. A poor content of Mg below0.05 wt % will render insufficient this effect, while an excessivecontent above 1.0 wt % brings about saturation of such an effect. Themost desirable content of Mg is from 0.3 to 0.8 wt %.

Zn contained in Al-Zn alloy gives it the sacrificial corrosion property.Zn content less than 0.05 wt % renders insufficient this effect, but ahigher Zn content more than 2.0 wt % undesirably accelerates corrosionof the alloy. Thus, the most desirable content of Zn is from 0.3 to 1.5wt %. Fe and/or Ni are necessarily contained in all the alloys mentionedabove in order to give them the high-temperature intercrystallinecorrosion resistance. Fe and Ni are equivalent to each other in respectof this effect so that at least one of them is to be contained. If bothof them are contained at contents less than 0.01 wt %, then such aneffect becomes negligible. Contrarily, if more than 0.3 wt % of Fe or Niis contained, then the low-temperature corrosion resistance becomespoor. Therefore, the most desirable contents of Fe and Ni are 0.03 to0.15 wt % and 0.03 to 0.15 wt %, respectively.

The balance of each alloy containing aforementioned necessary elementsis aluminum and unavoidable impurities contained therein. Purity ofaluminum metal is to be of 99.9% or higher in order to improve thelow-temperature corrosion resistance by decreasing said impurities to aslow content as possible. Such a high purity of aluminum will make iteasy to control the contents of Fe and/or Ni to fall within thedesirable range mentioned above. Aluminum metal of a purity of 99.99% orhigher is most desirable. Aluminum metal qualified as a grade of 99.9%or higher purity may be employed to control the aluminum content in thebalance to be 99.9% or more. Among the unavoidable impurities containedin the alloys, Cu makes poor the corrosion resistance of said alloys sothat its content should be 0.05 wt % or less.

The aluminum alloys in the invention may be used to manufacture thestructural members of heat exchangers wherein said alloys may beextruded into pipes or plates, or may be drawn after extruded.Alternatively, said alloy may be rolled at first into a shape of plateand thereafter seam-welded or upset-welded into a shape of pipe, ifnecessary. There is no limitation on what conventional method other thanthose known methods may be employed.

The aluminum alloys provided in the invention may be used as `bare`material to manufacture such a tubular element 1 as shown in FIG. 1.They are usable also to a composite material as shown in FIG. 2 whereinan outer surface of a core 2 made of such an alloy is covered with alayer 3 of a soldering agent which may be an-aluminum-silicon alloy,thus forming a different kind of a tubular element 1'. The layer 3 whichmay be applied to the core 2 by the cladding method or any othersuitable method will make it easy to solder the tubular element 1' tofin members not shown in FIG. 1. On the other hand, the pure-Al alloy,Al-Mg alloy and Al-Zn alloy provided in the invention are desirably usedto form an inner lining layer 4 as shown in FIG. 2, the lining layerbeing applied to the core 2 of the Al-Mg-Si alloy provided in theinvention.

It is to be noted that, as will become apparent from the Examplesdescribed below, the aluminum alloys provided in the invention so as tobe used to manufacture heat exchangers are excellent in theirlow-temperature corrosion resistance and also in their high-temperatureintercrystalline corrosion resistance. Thus, the aluminum alloys arehighly corrosion-resistant in a wide temperature range, so that they canbe advantageously used as the tubular element or the lining layer andprolong the life of the heat exchangers made of such an element andlayer.

Further, the Al-Mg-Si alloy which the invention provides is not onlyexcellent in its corrosion resistance as described above but also iseasy to work to the same degree as the known alloy "A3003". Besides, thestructural members made of Al-Mg-Si alloy are of a higher strength afterthey are soldered one another. Furthermore, the structural members canbe made thinner as to their wall thickness, thus decreasing theirweights and at the same time lowering their manufacture costs.

EXAMPLES

Examples of the aluminum alloys in the invention will now be describedin detail.

# Example 1

This example is for Al-Mg-Si alloys.

The aluminum alloys listed on Table 1 were molten, cast into desiredshapes and then subjected to homogenizing treatment. The thus preparedalloys were hot-rolled at 500° C., and subjected to intermediateannealing process for 2 hours at 370° C. before cold-rolled and finallyheat-treated at 600° C. for 5 minutes. Test pieces of 1.0 mm inthickness were made in this way as the tubular elements for heatexchangers.

The abovementioned test pieces were used to perform the following tests,i.e., soldering test, strength measurement of soldered members,corrosion tests on inner surfaces and on outer surfaces. The corrosiontests were carried out taking into account respectively the inner andouter environments in which the the members would be used.

                                      TABLE 1                                     __________________________________________________________________________    Composition (weight %)                                                        Alloys  Mg Si Mn Fe Ni Cu Ti Zn Al (Purity)                                   __________________________________________________________________________    Invention                                                                            1                                                                              0.77                                                                             0.36                                                                             0.98                                                                             0.27                                                                             -- -- -- -- Bal.(≧99.9%)                                  2                                                                              0.45                                                                             0.62                                                                             0.70                                                                             0.05                                                                             -- -- -- -- Bal.(≧99.9%)                                  3                                                                              0.56                                                                             0.58                                                                             1.12                                                                             0.08                                                                             -- -- -- -- Bal.(≧99.9%)                                  4                                                                              0.38                                                                             0.75                                                                             1.00                                                                             0.10                                                                             -- -- -- -- Bal.(≧99.9%)                                  5                                                                              0.18                                                                             0.85                                                                             0.45                                                                             -- 0.06                                                                             -- -- -- Bal.(≧99.9%)                                  6                                                                              0.43                                                                             0.67                                                                             0.55                                                                             -- 0.26                                                                             -- -- -- Bal.(≧99.9%)                                  7                                                                              0.42                                                                             0.44                                                                             1.40                                                                             0.08                                                                             0.20                                                                             -- -- -- Bal.(≧99.9%)                                  8                                                                              0.46                                                                             0.70                                                                             0.60                                                                             0.16                                                                             0.11                                                                             -- -- -- Bal.(≧99.9%)                           Reference                                                                            9                                                                              1.00                                                                             0.69                                                                             0.62                                                                             -- -- -- -- -- Bal.(≧99.9%)                                 10                                                                              0.37                                                                             1.21                                                                             0.84                                                                             0.35                                                                             -- -- -- -- Bal.(≧99.9%)                                 11                                                                              0.46                                                                             0.66                                                                             0.15                                                                             0.06                                                                             -- 0.09                                                                             -- -- Bal.(≧99.9%)                                 12                                                                              0.42                                                                             0.68                                                                             1.58                                                                             0.13                                                                             0.34                                                                             -- -- -- Bal.(≧99.9%)                                 13                                                                              0.06                                                                             0.18                                                                             0.98                                                                             -- -- -- -- -- Bal.(≧99.9%)                                 14                                                                              -- 0.21                                                                             1.11                                                                             0.53                                                                             -- 0.12                                                                             0.02                                                                             -- Bal. (*1)                                           15                                                                              -- 0.18                                                                             -- 0.16                                                                             -- -- -- 1.03                                                                             Bal. (*2)                                     __________________________________________________________________________     Notes:                                                                        *1 is the alloy "A3003", *2 is the alloy "A7072", and "Bal." denotes          "balance".                                                               

(1) Soldering Tests

Each test piece had a dimension of 50 mm in width and 50 mm in length soas to be soldered to an objective piece which comprised a core of thealloy A3003 and a soldering agent layer of "BA4045" cladded to bothsides of the core. The test piece 5 and the objective piece 6 werecombined to be of a T-shape as shown in FIG. 3. The soldering wascarried out using a fluoride flux within a nitrogen gas at 600° C. for 5minutes, and thereafter generation of fillets at soldered regions wasvisually inspected.

(2) Strength Measurement of Soldered Members

Tensile strength was carried out on other pieces of 50 mm in width and300 mm in length which had been heated in the nitrogen atmosphere at thesame time as the test pieces.

(3) Corrosion Test on Inner Surface

Test pieces of 40 mm in width and 70 mm in length were immersed in theASTM solution comprising "decuple water" plus 10 ppm of Cu⁺⁺, at 95° C.and 50° C. for 500 hours, respectively. Corrosion of these test pieceswas checked subsequently.

(4) Corrosion Test on Outer Surface

The saltwater-spraying test according to the standard of JIS-Z-2371 wasconducted for 1,000 hours for each of other test pieces which were 40 mmin width and 70 mm in length. Corrosion of these test pieces was checkedsubsequently.

Results obtained by these tests are given on Table 2.

As will be seen on Table 2, the alloy Nos. 1 to 8 provided by theinvention as the material to manufacture tubular elements of heatexchangers are readily soldered and easy to work to the same degree asthe known alloy "A3003", i.e., the reference No. 14. Further, the alloys(Nos. 1 to 8 ) proved sufficiently strong even after soldered andexcellent not only in their low-temperature corrosion resistance butalso in their high-temperature intercrystalline corrosion resistance.

                                      TABLE 2                                     __________________________________________________________________________               Strength after                                                                Soldered                                                                             Cor. Resist.  Cor. Resist.                                        Solder-                                                                            σ0.2                                                                       Rating                                                                            of In. Surf.(*3)                                                                            of Out. Surf.                                 Alloys                                                                              ability                                                                            (*1)                                                                             (*2)                                                                              (95° C.)                                                                      (50° C.)                                                                      (*4)                                          __________________________________________________________________________    Invention                                                                      1    Good 8.0                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             2    Good 7.7                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             3    Good 7.9                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             4    Good 8.0                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             5    Good 7.4                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             6    Good 8.2                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                             7    Good 7.5                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦  0.1 mm                                                                  P. ≦ 0.1 mm                             8    Good 8.6                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                            Reference                                                                      9(*5)                                                                              No good                                                                            14.0                                                                             Sup.                                                                              I/C 0.4 mm                                                                           P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                            10(*6)                                                                              No good                                                                            15.0                                                                             Sup.                                                                              P. ≦ 0.1 mm                                                                   P. 0.2 mm                                                                            P. ≦ 0.1 mm                            11    Good 7.3                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                                                                   P. 0.3 mm                                     12(*7)                                                                              Good 7.6                                                                              Sup.                                                                              P. ≦ 0.1 mm                                                                   P. 0.2 mm                                                                            P. ≦ 0.1 mm                            13    Good 4.0                                                                              Inf.                                                                              I/C 0.4 mm                                                                           P. ≦ 0.1 mm                                                                   P. ≦ 0.1 mm                            14    Good 4.3                                                                              Inf.                                                                              P. ≦ 0.1 mm                                                                   P. 0.2 mm                                                                            P. ≦ 0.1 mm                            15(*8)                                                                              Good 2.0                                                                              Inf.                                                                              Sf. 0.1 mm                                                                           Sf. 0.1 mm                                                                           Sf. 0.1 mm                                    __________________________________________________________________________     Notes:                                                                        *1; Kgf/mm.sup.2                                                              *2; "Sup." denotes `superior` indicating strength of 7 Kgf/mm.sup.2 or        more, and "Inf." denotes `inferior` indicating strength below 5               Kgf/mm.sup.2.                                                                 *3; Corrosion resistance of inner surface, and                                *4; Corrosion resistance of outer surface, wherein "P. " denotes `pinhole     corrosion, "I/C" denotes `intercrystalline` corrosion, and "Sf." denotes      `surface` corrosion accompanied by many corrosive products.                   *5; Ununiformed generation of fillets was observed.                           *6; Intercrystalline erosion was observed near the fillets.                   *7; Generation of coarse crystals was observed.                               *8; Surface corrosion with many corroded products.                       

In contrast with the alloys in the invention, the reference alloy Nos. 9and 13 which do not contain Fe nor Ni are inferior to those in theinvention in the high-temperature intercrystalline corrosion. The otherreference alloy Nos. 10 and 12 containing excessive amounts of Fe and/orNi are insufficient in their low-temperature corrosion resistance.Solderability of the reference alloy Nos. 9 and 10 which containsexcessive amounts of Mg or Si is worse than those in the invention.Lower corrosion resistance of outer surface was observed for the otherreference alloy No. 11 which contained less amount of Mn and anexcessive amount of Cu as one of the impurities. The reference alloy No.12 containing an excessive amount of Mn has proved bad in itsworkability due to generation of an intermetallic compound indicatedwith "Al-Fe-Mn". The further reference alloy Nos. 13 and 14, the latterbeing A3003, were found inferior to the other alloys in the strengthafter soldered.

# Example 2

This example is for the pure-Al alloys.

The aluminum alloys listed on Table 3 were molten, cast into desiredshapes and then subjected to homogenizing treatment. The thus preparedalloys were hot-rolled at 500° C., and subjected to intermediateannealing process for 2 hours at 370° C. before cold-rolled and finallyheat-treated at 600° C. for 5 minutes. Test pieces of 1.0 mm inthickness were made in this way as the tubular elements for heatexchangers.

Corrosion tests were performed for the test pieces in the followingmanner. Namely, the test pieces of 40 mm in width and 70 mm in lengthwere immersed in the ASTM solution comprising "decuple water" plus 10ppm of Cu ⁺⁺, at 95° C. and 50° C. for 500 hours, respectively.Corrosion of these test pieces which had been immersed in the solutionwas checked subsequently, and gave the results listed on Table 3.

It will be seen from Table 3 that the aluminum alloy Nos. 16 to 20provided by the invention to manufacture heat exchangers provedcorrosion-resistant with their excellent low-temperature corrosionresistance and high-temperature intercrystalline corrosion resistance.The reference alloy No. 21 lacking Fe and Ni proved inferior to them inthe high-temperature intercrystalline corrosion resistance. The otherreference alloy No. 22 rich in Ni was found bad in its low-temperaturecorrosion resistance, whereas the further reference alloy 23 rich in Cuas one of the unavoidable impurities proved inferior to the alloys inthe invention in both types of the corrosion resistance.

                                      TABLE 3                                     __________________________________________________________________________    Composition (wt %)       Corrosion resistance                                 Alloys                                                                              Fe  Ni  Cu  Al (purity)                                                                          at 95° C.                                                                     at 50° C.                              __________________________________________________________________________    Invention                                                                     16    0.02                                                                              --  --  Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          17    0.28                                                                              --  --  Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          18    --  0.02                                                                              --  Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          19    --  0.27                                                                              --  Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          20    0.11                                                                              0.14                                                                              --  Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          Reference                                                                     21    --  --  --  Bal.(≧99.9%)                                                                  I/C 0.4 mm                                                                           Pin. ≦ 0.1 mm                          22    --  0.38                                                                              --  Bal.(≧99.9%)                                                                  Pin. 0.2 mm                                                                          Pin. 0.3 mm                                   21    0.05                                                                              --  0.14                                                                              Bal.   Pin. 0.3 mm                                                                          Pin. 0.3 mm                                   __________________________________________________________________________     Notes:                                                                        "Bal." denotes `balance`, "Pin. "  denotes `pinhole`. and "I/C" denotes       `intercrystalline corrosion`.                                            

# Example 3

This example is for the Al-Mg alloys.

Aluminum alloys listed on Table 4 were formed into test piecesrepresentative of the tubular elements in heat exchangers, on the samecondition as that in Example 2.

The test pieces were subjected to the same corrosion tests as those inExample 2, the results obtained being listed on Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Composition (wt %)       Corrosion resistance                                 Alloys                                                                              Mg Fe Ni Cu Al (purity)                                                                          at 95° C.                                                                     at 50° C.                              __________________________________________________________________________    Invention                                                                     24    0.50                                                                             0.18                                                                             -- -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          25    0.98                                                                             -- 0.23                                                                             -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          26    0.22                                                                             0.10                                                                             -- -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          27    0.65                                                                             0.16                                                                             0.11                                                                             -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          Reference                                                                     28    0.80                                                                             -- -- -- Bal.(≧99.9%)                                                                  I/C 0.4 mm                                                                           Pin. ≦ 0.1 mm                          29    0.68                                                                             0.42                                                                             -- -- Bal.(≧99.9%)                                                                  Pin. 0.2 mm                                                                          Pin. 0.2 mm                                   30    0.53                                                                             -- 0.05                                                                             0.14                                                                             Bal.   Pin. 0.3 mm                                                                          Pin. 0.3 mm                                   __________________________________________________________________________     Notes:                                                                        "Bal." denotes `balance`, "Pin. " denotes `pinhole`, and "I/C" denotes        `intercrystalline corrosion`.                                            

It will be seen from Table 4 that the aluminum alloy Nos. 24 to 27provided by the invention to manufacture heat exchangers provedcorrosion-resistant with their excellent low-temperature corrosionresistance and high-temperature intercrystalline corrosion resistance.The reference alloy No. 28 lacking Fe and Ni proved inferior to them inthe high-temperature intercrystalline corrosion resistance. The otherreference alloy No. 29 rich in Fe was found bad in its low-temperaturecorrosion resistance, whereas the further reference alloy 30 rich in Cuas one of the unavoidable impurities proved inferior to the alloys inthe invention in both types of the corrosion resistance.

# Example 4

This example is for the Al-Zn alloys.

Aluminum alloys listed on Table 5 were formed into test piecesrepresentative of the tubular elements in heat exchangers, on the samecondition as that in Example 2.

The test pieces were subjected to the same corrosion tests as those inExample 2, the results obtained being listed on Table 5.

It will be seen from Table 5 that the aluminum alloy Nos. 31 to 34provided by the invention to manufacture heat exchangers provedcorrosion-resistant with their excellent low-temperature corrosionresistance and high-temperature intercrystalline corrosion resistance.The reference alloy No. 35 lacking Fe and Ni proved inferior to them inthe high=temperature intercrystalline corrosion resistance.

                                      TABLE 5                                     __________________________________________________________________________    Composition (wt %)       Corrosion resistance                                 Alloys                                                                              Zn Fe Ni Cu Al (purity)                                                                          at 95° C.                                                                     at 50° C.                              __________________________________________________________________________    Invention                                                                     31    1.01                                                                             0.08                                                                             -- -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          32    1.50                                                                             -- 0.17                                                                             -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          33    0.53                                                                             0.27                                                                             -- -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          34    1.15                                                                             0.16                                                                             0.11                                                                             -- Bal.(≧99.9%)                                                                  Pin. ≦ 0.1 mm                                                                 Pin. ≦ 0.1 mm                          Reference                                                                     35    1.03                                                                             -- -- -- Bal.(≧99.9%)                                                                  I/C 0.4 mm                                                                           Pin. ≦ 0.1 mm                          36    0.51                                                                             0.05                                                                             -- 0.14                                                                             Bal.   Pin. 0.3 mm                                                                          Pin. 0.3 mm                                   __________________________________________________________________________     Notes:                                                                        "Bal." denotes `balance`, "Pin. " denotes `pinhole`, and "I/C" denotes        `intercrystalline corrosion`.                                            

The other reference alloy No. 36 rich in Cu as one of the unavoidableimpurities proved inferior to the alloys in the invention in both typesof the corrosion resistance.

What is claimed is:
 1. A material for forming heat exchangers, thematerial consisting of: 0.1 to 0.8 wt % of Mg; 0.2 to 1.0 wt % of Si;0.3 to 1.5 wt % of Mn; 0.01 to 0.3 wt % of Fe; and 0.01 to 0.3 wt % ofNi, wherein the balance of material consists essentially of aluminum ofpurity of 99.9% or higher and 0.1 wt % or less of unavoidable impuritiescontained therein, and the content of Cu as one of the impurities is0.05 wt % or less, said material being further characterized by the factthat the pinhole corrosion of the material is less than or approximatelyequal to 0.1 mm when immersed in an ASTM solution comprising decuplewater plus 10 ppm of Cu⁺⁺ at 95° C. or 50° C. for 500 hours.
 2. Amaterial as defined in claim 1, wherein the material contains 0.2 to 0.5wt % of Mg, more than 0.4 wt % but up to 0.7 wt % of Si, 0.5 to 1.2 wt %of Mn, 0.03 to 0.15 wt % of Fe and 0.03 to 0.15 wt % of Ni.